Heat exchange system



Dec. 3l, 1957 F. Lus'rwERK ETAL HEAT EXCHANGE SYSTEM Filed May 3, 1954 HIHUIH United States PatentL amasar.

rmATfExerrANGErsYsnEr/n Ferdinand -Lustwerk, Lincoln,.. Harold. S.. `lVIikley, Blmont,. and 'EnestlPfNellml'li Lincoln, Mass., assignors, by`mesn'e assignments, td'Rlieem Manufacturing Company, a corporationofCliftrnia Application Mayr .11954;Serial .Mme-4272049;

The present invention is in the field of heat exchange and relates .in particulartto coolingsysternsfor dissipatingheat to an.evaporating liquid. importantapplication of the. invention is in the ,construction 'and operation of evaporative -condenserspf-thetype commonly ernployed in refrigeration andtaircondifionin'g systems.`

In general a coolingsystem bingsa fluid' to. be `cooled into `thermal contact with .a coolantliuid' Ioilower teme perature to whichv heatds. transferred. 'I`hi's",invention is primarily yconcerned lwithpystems .npwhichl heat is transferred tothe coolant duid-.through tins-.and fits object is to improve the. ecie'ncygof-heat transferso that a smaller and less expensive heat exchanger: v.maybe used for a given job,.and so thatlesspowerislrequired to bring the fluids into i thermal contact,

In systems of this invention the fluid 'to be coolecllis brought into thermal contact with a film of liquid over which is Vpassed a: stream.-.of..ga,rs,.I byY .lio-wing. -gthe fluid to be cooled through a `conduitpfthermally conductive material While"maintain'ing `th'e"liql.tid"filr'n on fins in thermal ContactA .with.the,.conduitrv The condutxis `desirably provided..with a largeintennal: carea, preferably by means1 of longitudinal..internalaflns'amountedinfthe annular region. betweeny the yconduitand fan internalx con- -centric tube. Coolingis providedbysprayingforfotherwise supplyingy the. Vtins, .with..an.evaporative liquid, {generally water, while a stream of air or other gas is flowed past them.

A significant improvement has been found to result if the fins are inclined from the horizontal, and the gas stream is flowed past them, with the lower edges of the fins upstream from the upper edges, at a velocity substantially counteracting gravitational flow of the liquid across the fins. This greatly increases the `amount of liquid contained on the fins and also maintains this liquid in a rippling and agitated condition, with the result of increasing substantially the rate of heat transfer.

The velocity of the gas stream and the inclination of the ns are of course interrelated, and it has also been found that the angle of the ns to the direction of the gas stream should not be so great that the aerodynamic action of the ns interferes with the gas flow along their surfaces. Best operation results if the gas stream is flowed substantially parallel to lthe tins with its velocity controlled to prevent substantially the downward free ow of the liquid across the tin surfaces. This condition may be seen to lexist when 4the liquid on the ns is in a rippling and agitated condition and ows off them from both the upper and lower edges.

A representative and preferred embodiment of this invention is described in detail below, reference being made to the drawings in which:

Fig. l is a cross-sctional side elevation showing a cooling system embodying this invention.

Fig. 2 is an edge view of a tin illustrating the behavior of the liquid lm under preferred conditions.

Fig. 3 is a cross-sectional end view showing the pre- 2,817,959V Patented Dec. 31, 1957 21." ferred construction of the conduit'for, the liquid 'robe cooled.

In the illustrated embodiment a heat yexchanger 10 having several external spaced parallel tins 12 is mounted in a generally horizontal air duct 14 withthe iins 12 inclined from the horizontal at an angle' to the axis of the duct. A spray head 16 is mounted onapipe 18 inthe duct to direct a spray of water against the fins and .a fan 20 .is mounted on bracketsy 22 within the` duct to create an air stream through the du'ct in the .direction such that the lower edges of the fins 12 are upstream from vthe upper edges, as indicated by the arrows. Water draining from the ns isfcollected and .removed by sloping the bottom of the duct 14 downwardly to a drain conduit 23.

The heatv exchanger 10 (as best shown by Fig. 2) con Veniently consists of a conduit 24 for the. fluid to `be cooled, to the outside Walls -ofwhich are .mounted the tins 12. The inside of the conduit 24 is provided with longitudinal fins 26 mounted between and in thermal contact withthe inner wall of conduit 24 and the outer w-all of an inner concentricY tube 28. The internal ns 26 are conveniently formed by curving a corrugated sheet yof conductive material to occupy the annularspace between lthe conduit 24 and tube 28, with the corrugations extending between them. This construction is conveniently provided by loosely assembling the .corrugated sheet defining fins 26 between the conduit 24 and tube 28, then expanding the-tube, as by drawing a mandrel through it, to press the ridges -of the corrugatio'ns into tightcontact with the .enclosing Walls, as disclosed in greater detail in United StatesPatent No. 2,611,587. The fluid to be cooled may be passed through both the conduit'24 and tube 28,'although itis preferable to dispense with the center tube 28 as a lconduit for fluid, lsince Asomewhat greater efficiencies may thus be obtained.

In operation, the yiluid to be cooled,y for instance cornpressed refrigerant gas, is owed through theA conduit 24,v while water is sprayed from the `spray head 16 vonto the lins yand an air stream past the fins iscirculated by the fan 20 at a velocity to restrain the free downward gravitational How of water from the iins and to maintain the Water as a rippling and agitated film flowing from both edges of the ns, as shown in Fig. 3.

Upon observation of the device in operation it will also be observed that the combination of gravity and the countercurrent of air produces, in addition to an agitated repelling of the water, a transient plugging of the space between adjacent ns. The water plugs dance back and forth at random between the ns, moving not only back and forth but also laterally with respect to the direction of air ow. The water plugs do not appear to be permanent but are blown out after a few seconds. It is not known whether this intermittent plugging and unplugging of the passages between adjacent fins contributes to the efficiency of heat exchange, although it does appear that maximum eii'iciency is obtained when the velocity of the air and the inclinati-on of the lins is so adjusted that the phenomena of intermittent plugging is observed.

In a typical embodiment such conditions exist with an air stream flowing horizontally at a Velocity of 1000 feet per minute against ins inclined from the horizontal by between about 5 and l5 degrees. However, as pointed out above both the inclination of the tins and the velocity of the air along their surfaces may be varied complementarily to establish Ithe desired conditions in the liquid lm `on the fins, as may be detected by observation lof the behavior of the film of liquid.

Although this invention has been described in detail with reference to a preferred embodiment it is contemplated that modications will readily occur to those skilled in the art, and that such modifications may be made without departing from the 'scope of the invention.

Having thus disclosed our invention and described in detail a preferred embodiment thereof, we claim and desire to secure by Letters Patent:

l. A heat exchange system comprising conduit means in thermal contact with fins, said fins being inclined about 4 to 15 degrees from the horizontal, means for supplying a liquid to said fins, and means for passing a substantially horizontally directed stream of gas past said hns from the lower edges to the upper edges at a velocity along the surface of the tins substantially counteracting gravitational dow of the liquid across said fins and maintaining the liquid thereon in a layer.

2. The method of cooling a fluid in a conduit and in thermal contact with a iin exteriorly of the conduit and inclined about 4 to 15 degrees from the horizontal, cornprising supplying a water lrn upon said tin, and passing a substantially horizontally directed stream of gas past said fin from the lower edge to the upper edge at a velocity along the water film surface substantially counteracting gravitational flow of the lm on said fin.

3. A heat exchange system comprising conduit means in thermal contact with fins, said fins being inclined up* wardly from the horizontal substantially from the front to the rear edges thereof, means for supplying a liquid to said iins in an amount to cover same with a solid film of the liquid, and means for passing a stream of gas past said tins from the front edges to the rear edges at a velocity along the surface of the fins substantially overcoming the free downward gravitational ilow of the liquid upon said fins.

4. A heat exchange system comprising conduit means in thermal contact with fins, said fins being inclined upwardly from the horizontal substantially from the front to the rear edges, spray means for covering the fins with a solid layer of liquid, and means for passing a substantially horizontally directed stream of gas past said fins from the front edges to the rear edges at a velocity along the surface of the tins substantially overcoming gravitational flow of the liquid across said ns and thereby provide a continuously flowing layer of liquid on said hns.

5. The method of cooling a fluid in a conduit comprising passing said fluid in the conduit in thermal contact with a fin inclined from the horizontal, supplying evaporative liquid upon said n in an amount to completely cover same and ow freely on the lin, and passing a stream of gas across said n from the lower edge to the upper edge at a velocity along the surface of the liquid on the n substantially restraining the `free, gravitational flow of thc liquid upon the fin and to maintain the water as a rippling and agitated film owing from both the upper and lower edges thereof.

6. In an evaporative condenser for cooling liquids, conduit means in thermal contact with fins, said fins being inclined from the horizontal and spaced from each other for the ow of air therebetween, means directing liquid upon the fins from adjacent the lower edge thereof in an amount to completely cover same and flow thereupon, and means for moving a stream of air between said fins from the lower to the upper edges thereof at a velocity substantially overcoming the free gravitational flow of the liquid on the fins.

7. The method of cooling a fluid in a conduit comprising passing said fluid in the conduit in thermal contact with a fin inclined from the horizontal, continuously supplying an evaporative liquid upon said n in an amount sufficient to cause said liquid to normally gravitationally flow towards the lower edge of said tin, and at the same time passing a stream of gas across said fin from the lower to the upper edge thereof at a velocity suicient to substantially overcome the gravitational ow of liquid whereby liquid willow over both the upper and lower edges of the fin, the amount of liquid supplied being sufficient to have substantially the entire upper surface of said iin continuously covered with liquid notwithstanding evaporation of said liquid and the overflowing thereof from the fin edges.

References Cited in the file of this patent UNITED STATES PATENTS 1,955,269 Anetsberger c Apr, 17, 1934 2,093,691 Buder Sept. 2l, 1937 2,228,550 Young Ian. 14, 1941 2,278,242 Chapman Mar. 3l, 1942 2,495,002 Hart Jan. 17, 1950 2,611,587 Boling Sept. 23, 1952 

